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From: Waiman Long <longman@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Juergen Gross <jgross@suse.com>,
	Yi Sun <yi.y.sun@linux.intel.com>,
	linux-kernel@vger.kernel.org, x86@kernel.org, tglx@linutronix.de,
	chao.p.peng@intel.com, chao.gao@intel.com,
	isaku.yamahata@intel.com, michael.h.kelley@microsoft.com,
	tianyu.lan@microsoft.com, "K. Y. Srinivasan" <kys@microsoft.com>,
	Haiyang Zhang <haiyangz@microsoft.com>,
	Stephen Hemminger <sthemmin@microsoft.com>,
	"mingo@redhat.com" <mingo@redhat.com>,
	Will Deacon <will.deacon@arm.com>
Subject: Re: [PATCH v1 2/2] x86/hyperv: make HvNotifyLongSpinWait hypercall
Date: Mon, 22 Oct 2018 14:01:47 -0400	[thread overview]
Message-ID: <0f36b234-fa4e-d52f-735c-078ddeab6720@redhat.com> (raw)
In-Reply-To: <20181022173144.GB3109@worktop.c.hoisthospitality.com>

On 10/22/2018 01:31 PM, Peter Zijlstra wrote:
> On Mon, Oct 22, 2018 at 01:27:27PM -0400, Waiman Long wrote:
>
>>>> I agree with Juergen on that. I would suggest rename the
>>>> vcpu_is_preempted hook into a more generic vcpu_stop_spinning, perhaps,
>>>> so different hypervisors can act on the information accordingly. Adding
>>>> an extra parameter is fine.
>>> No; no extra parameters. vcpu_is_preempted() is a simple and intuitive
>>> interface. Why would we want to make it complicated?
>> Hyperv seems to do it in a somewhat different way by looking at the spin
>> counter and decide if it should continue. I don't know why they do that
>> and what advantage it has.
>>
>> The current patch is definitely not OK. A revised patch that makes use
>> of an existing paravirt hook will be more acceptable. Again, I would
>> like to see some performance figure and why they do it this way to see
>> if it is worthwhile to change the existing interface.
> Note that there are vcpu_is_preempted() users that are not in a
> spin-loop.

You are right. I forgot about that. In that case, someone has to prove
that using an alternative way to stop spinning really has a performance
advantage compared to what we already have today.

Cheers,
Longman


  reply	other threads:[~2018-10-22 18:01 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-10-19 13:13 [PATCH v1 0/2] Enable HvNotifyLongSpinWait for Hyper-V Yi Sun
2018-10-19 13:13 ` [PATCH v1 1/2] x86/hyperv: get spinlock retry number on Hyper-V Yi Sun
2018-10-19 13:13 ` [PATCH v1 2/2] x86/hyperv: make HvNotifyLongSpinWait hypercall Yi Sun
2018-10-19 14:20   ` Juergen Gross
2018-10-22  1:53     ` Yi Sun
2018-10-22  7:32       ` Juergen Gross
2018-10-22 16:31         ` Waiman Long
2018-10-22 17:15           ` Peter Zijlstra
2018-10-22 17:27             ` Waiman Long
2018-10-22 17:31               ` Peter Zijlstra
2018-10-22 18:01                 ` Waiman Long [this message]
2018-10-23  2:57             ` Yi Sun
2018-10-23  8:51               ` Peter Zijlstra
2018-10-23  9:33                 ` Yi Sun
2018-10-31  1:54                   ` Yi Sun
2018-10-31 14:10                     ` Peter Zijlstra
2018-10-31 15:07                       ` Waiman Long
2018-10-31 17:15                         ` Peter Zijlstra
2018-11-01  3:20                           ` Yi Sun
2018-11-01  8:59                             ` Peter Zijlstra
2018-11-01 12:59                             ` Waiman Long
2018-11-05  6:54                               ` Yi Sun
2018-10-24 16:53   ` Michael Kelley
2018-10-25  2:23     ` Yi Sun
2018-10-31  2:06     ` Yi Sun

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